body {
    background-color: whitesmoke; 
}

.nav-main {
    position: fixed;
    left: 0;
    top: 0;
    width: 100%;
    height: 60px;
    background-color: white;
    display: flex;
    flex-wrap: wrap;
    z-index: 1000;
}

.btn-toggle-nav {
    width: 60px;
    height: 100%;
    background-color: skyblue;
    background-image: url("menu.png");
    background-repeat: no-repeat;
    background-size: 40%;
    background-position: center;
    cursor: pointer;
}

.btn-toggle-nav:hover {
   opacity: 0.5;
}

.nav-main ul {
    display: flex;
    flex-wrap: wrap;
    padding-left: 15px;
}

.nav-main ul li {
   list-style: none;
   line-height: 30px;
}

.nav-main ul li a {
    display: block;
    height: 100%;
    padding: 0 10px;
    text-transform: uppercase;
    text-decoration: none; 
    color: black;
    font-family: Arial, Helvetica, sans-serif;
    font-size: 16px;
}

.nav-sidebar {
    position: fixed;
    left: 0;
    bottom: 0;
    width: 50px;
    height: calc(100vh - 60px);
    padding: 0 5px;
    background-color: #1b1b1b;
    z-index: 1000;
    transition: all 0.3s ease-in-out;
    -webkit-transition: all 0.3s ease-in-out;
    -moz-transition: all 0.3s ease-in-out;
    -ms-transition: all 0.3s ease-in-out;
    -o-transition: all 0.3s ease-in-out;
}

.nav-sidebar ul {
    padding-top: 15px;  
    overflow: hidden;
    visibility: hidden;
}

.nav-sidebar ul li {
    line-height: 60px;
    list-style: none;
}

.nav-sidebar ul li span, .nav-sidebar ul li a {
    display: block;
    height: 60px;
    padding: 0 10px;
    text-decoration: none;
    text-transform: uppercase;
    color: #FFF;
    font-family: Arial, Helvetica, sans-serif;
    font-size: 16px;
    white-space: nowrap;
    opacity: 0;
    transition: all 0.3s ease-in-out;
}

.nav-sidebar ul li a:hover {
    background-color: #222;
}